1. Field of the Invention
The present invention relates to a zoom lens and, more particularly, to a zoom lens suitable as an imaging lens for use in an image pickup apparatus such as a monitoring camera, digital camera, video camera, or broadcasting camera.
2. Description of the Related Art
An image pickup apparatus using a solid-state image sensor is required to include an imaging lens having a high optical performance capable of corresponding to a high resolution of the solid-state image sensor.
Also, an imaging lens for a monitoring camera is required to be able to pick up an image with a wide range by a single monitoring camera, be a zoom lens having a high zoom ratio, be readily installable, be small so as to be inconspicuous, and have a small f-number so as to be able to perform picking up an image even in a dark environment.
As an arrangement that readily implements a wide-angle, small-sized zoom lens, a zoom lens in which a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, and a third lens unit having a negative refractive power are arranged in this order from an object side to an image side is known. For example, Japanese Patent Application Laid-Open No. 2008-151947 and U.S. Pat. No. 8,031,410 have disclosed zoom lenses in each of which a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, and a third lens unit having a negative refractive power are arranged in this order from an object side to an image side.
However, to implement a zoom lens that simultaneously satisfies a wide angle of field, small size, large aperture, and high zoom ratio by using the above-mentioned, three-unit zoom lenses, it is necessary to appropriately set, e.g., the refractive power of each lens unit forming the zoom lens, the lens configuration of each lens unit, and the moving amount of each lens unit during zooming.